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Clock ticking: GMT could be history, Leading scientists around the world are meeting in Britain to consider a proposal that could eventually see Greenwich Mean Time relegated to a footnote in history.

While each country has (in broad terms) historically had distinct measurements for distance, weights etc the method of splitting the day into 24 hours, one hour into 60 mins and one minute into 60 seconds seems to be the only one in use, and indeed to me the only one I know of. This non-metric measurement of time is far from ideal, but what other comparably accurate methods have been used historically?

"The origin of our time system of 24 hours in a day with each hour subdivided into 60 minutes and then 60 seconds is complex and interesting," says Dr Nick Lomb, consultant curator of astronomy, from the Sydney Observatory.

Our 24-hour day comes from the ancient Egyptians who divided day-time into 10 hours they measured with devices such as shadow clocks, and added a twilight hour at the beginning and another one at the end of the day-time, says Lomb.

"Night-time was divided in 12 hours, based on the observations of stars. The Egyptians had a system of 36 star groups called 'decans' — chosen so that on any night one decan rose 40 minutes after the previous one.

"Tables were produced to help people to determine time at night by observing the decans. Amazingly, such tables have been found inside the lids of coffins, presumably so that the dead could also tell the time."

In the Egyptian system, the length of the day-time and night-time hours were unequal and varied with the seasons.

"In summer, day-time hours were longer than night-time hours while in winter the hour lengths were the other around," says Lomb.

Ancient Babylonians: hours and minutes

The subdivision of hours and minutes into 60 comes from the ancient Babylonians who had a predilection for using numbers to the base 60. For example, III II (using slightly different strokes) meant three times 60 plus two or 182.

"We have retained from the Babylonians not only hours and minutes divided into 60, but also their division of a circle into 360 parts or degrees," says Lomb.

"What we have not retained is their division of a day into 360 parts called 'ush' that each equalled four of minutes in our time system."

Lomb says it's likely that the Babylonians were interested in 360 because that was their estimate for the number of days in a year. Their adoption of a base 60 system was probably allowed them to make complex calculations using fractions.

Ancient Chinese

The ancient Chinese used a dual time system where they divided the day into 12 so-called, 'double hours', originally with the middle of the first double hour being at midnight.

They also had a separate system in which a day was divided into 100 equal parts called 'ke', that are sometimes translated as 'mark' into English.

"What complicated this arrangement was that the two systems did not mesh well since there were a non-integral number of ke in each double hour, specifically 8 1/3. Because of this inconvenience, much later on, in the year 1628 of our era, the number of ke in a day was reduced to 96," says Lomb.

Metric time?

In 1998, the Swiss watch company Swatch introduced the concept of a decimal Internet Time in which the day is divided into 1000 'beats' so that each beat is equal to 1 minute 26.4 seconds. The beats were denoted by the @ symbol, so that, for example, @250 denotes a time period equal to six hours.

"So far this system has not caught on," says Lomb.

"For each country the immense cost and difficulty in switching over to this or another metric time system would be enormous, possibly as great, if not greater, than it was for Australia to switch to decimal currency back in 1966," he says.

"The insurmountable difficulty though would be the prior hurdle of getting each country in the world both to agree to change and to agree on a common system of decimal time. I think that I am safe in stating that there will be no change from the present system of time measurement in the foreseeable future."

Keeping timeWhile our units for measuring time seem to be here to stay, the way we measure time has changed significantly over the centuries. The Ancient Egypitians used sundials and waterclocks, as did several civilisations after them. Hourglasses were also an important time-keeping device before the invention of mechanical and pendulum clocks. The development of modern quartz watches and atomic clocks has enabled us to measure time with increasing accuracy.

Today, the standard definition for time is no longer based on the rotation of the Earth around the Sun, but on atomic time. A second is defined as: "9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."

Hammer :

Dr. Rey Tiquia :

16 Nov 2011 8:23:23pm

The supposed 'irreconcilability' between the Chinese 'double-hour time system and the 'ke' system was 年in actuality reconciled by the use of the sexagenary 'gan zhi'(stem and branch)counting system that the premodern Chinese used to mark the passage of the years 'nian' 年, months'yue' 月, days'ri' 日 and double-hour time periods'shi chen‘ 時辰.The 'stem'has a decimal base while the 'branch' has a duodecimal base. And the two were sequentially combined to form 60 digits.

Dr. Rey Tiquia :

19 Nov 2011 9:09:51pm

Hi Jason,

Actually I have just completed a presentation last Wednesday ( Nov. 16, 2011) before the American Anthropological Association Annual Conterence here in freezing Montreal on the 'Temporo Spatial Considerations in Acupuncture for Pain Translating Causal Mechanisms'. In the presentation, I presented a case study on the use of chronoacupuncture (Zi Wu Liu Zhu) in clinically dealing sucessfully with pain resulting from herniation of the cervical vertebrae. The use of chronoacupuncture method of the 'Eight Techniques of the Sacred Turtle' (ling gui ba fa) and the choice of acupuncture points was made on the basis of the a calibrated Chinese calendar -the Australian Chinese Calendar. Which means the use of chronoacupuncture was made to enhance the flow of 'qi' or energy and blood of this particular patient. Hence, in the Southern Hemisphere in Australia the temporo-spatial movement of energy or 'qi' can now be accessed .

S Hughes :

Nick Lomb :

18 Nov 2011 10:34:52am

Good point S. Hughes. Astronomers for some purposes such as recording observations of variable stars use Julian Dates that represent a continuous count from about 6700 years ago. Times are represented as decimals of a day from 12 noon at Greenwich, eg as I am writing this the Julian Date is 2455883.522222. Though invaluable for astronomical calculation, Julian Dates are unlikely to be accepted for use by the general community.

Tamaresque :

Tony :

16 Nov 2011 6:57:31pm

This item is great but I am not sure it answers the question it poses. Why are there 24 hours in a day?Although the answer can be drawn from this as "simply because it is a helpful convention" it fails to explain the link between the second and the pendulum then that the resultant 86400 seconds a day are so nicely divisible by 24 or 12 and 60 then 60. The Numbers selected are also ideal for people planing their days minutes or seconds because 24 is divisible by 2,3,4,6 and 12 then 60 by 2,3,4,5,6... Not to mention 360 which is comfortably divided by 2,3,4,5,6,-,8,9,10,15,20,30,40,45,90,180 and more. It is again not a coincidence that on the compass 360 degrees is also divided into minutes and seconds.

Nick Lomb :

18 Nov 2011 10:46:45am

You are right Tony. The 24 hour system would not have remained in use if it had not been a convenient scheme. Note though that the link between the second and the pendulum of a longcase or grandfather clock is that the length of the pendulum is made to be 0.994 metre so that it beats once a second (2 second oscillation). Different lengths of pendulum give different oscillation times. And, of course, 86400 is the product of the 24 hours in a day, the 60 minutes in an hour and 60 seconds ina minute. Hence it is automatically divisable by those numbers.

Ryszard :

18 Nov 2011 6:42:19pm

"length of the pendulum is made to be 0.994 metre"

AHA! Bradman strikes again! Was he Sumerian, or "some Aryan"?[...]

Interesting article. Thanks. A friend who collects clocks told me that the early (Western) clocks had no minute hands & that there was no standardisation of the hour shown on the clocks, making appointment-fixing difficult to say the least. Did the ancients have a standard for "telling the time", & if so, how did we lose it?

Max Prince :

16 Nov 2011 7:43:51pm

Hi Nick, I'm so glad that you haven't completely retired. It was always great to talk to you when I was Principal of forst St P.S.Your 24 hour item is really great. I'll pass it on to my grandkids. The ancient Egyptians invented the theory of one god and now the idea of a 24 hour day.Keep up the good work Nick.

Nick Lomb :

18 Nov 2011 10:49:41am

Great to hear from you Max and I am pleased you found the item of interest. I have kept working and being busy. My new book on the transit of Venus is being launched at Sydney Observatory on Thursday 24 November 2011.

Amacha :

17 Nov 2011 6:03:37pm

To make right triangle it is possible to use 12 equal lengths to make a 3-4-5 triangle, which could be used by the Egyptians to survey buildings, cut stone , etc. I have always thought it would be natural to lay out 12 equal lenths in a circle to define the periods in a shadow clock, thus 12 hours of daylight, or 24 hours in an day/night.

RN :

18 Nov 2011 11:35:01am

If take old civilizations idea that day and year are similar - every 6 months the eclipses start a series of 6 new and 6 full moons. Gives idea that natural division of year is 6, 12, 24. Then apply to day as well as year.

Everolimus :

18 Nov 2011 2:54:00pm

Why did the ancient Babylonians or was it the Sumerians, use the base 60 for their calculations? What is magic with this number? Why did they choose it over other numbers?The answer is simple. They had the original digital calculator to help them with their calculations.Hold up your hand. Count the bones in your 4 fingers. I have twelve. Multiply this by the number of digits and you should get sixty.

Eighth Aero :

ep7 :

22 Nov 2011 3:41:39am

Authors Knight and Butler in their groundbreaking book "Civilization One" give one of the best interpretations of how we now have our time, area, volume and other current-day measurement systems from the Sumarians, Babaloyians, Egyptians, et al.

Althought the authors lean to the ancient astronaut theory, their work on how we have our current measurement systems is amazing into itself.

Read the first 50 pages, and skip the rest if it does not interest you.

Digger :

31 Jan 2012 4:54:20pm

Hi Tony, I had not heard that explaination before. But I have another similar. In the Army when you make camp in a defensive position, an enemy is most likely to make an attack on your position at Dusk or Dawn. We would "Stand Too" ( a period of silence and extra vigenace during this period. We were told that the way to tell when dusk was done was to wear one green and one red band on your wrist. when the light had faded enough that you could not tell the difference between them it was time to stand down!

Robert :

22 Nov 2011 4:43:37pm

Minute comes from the Latin minu -to make smaller. So minute (and minute) are a little bit, of an hour in case of time. A second is the second little bit. Just wondering if the Romans borrowed the idea of breaking an hour up into 60 little bits or just thought it was a good idea as well.

Dave :

04 Dec 2011 10:24:00am

As far as I understand it the Romans were extremely good at borrowing ideas from different cultures. Their strength was in public speaking which they considered the pinicle of civilization. Mundane things such as farming and manufacturing were looked down upon as being slaves work. Makes you wonder how they lasted so long.